(1) Field of the Invention
This invention relates to a highly compressible soft asbestos free gasket material and a method of manufacture thereof. Specifically, this invention is directed to a gasket material which is comprised of fibrillated aramid fibers, diatomaceous earth, a phenolic resin and either a polyethylacrylic or polybutylacrylic latex alone or in combination with various processing agents, the gasket material being free of asbestos fibers.
(2) Description of the Prior Art
For many years, gasket materials for many important uses have contained asbestos fibers. Asbestos fibers have been uniquely suited for gasket materials because of their ability to impart to the gasket material critically important performance and structural features such as heat resistance, good sealability and desirable mechanical properties such as compressibility, creep resistance and tensile strength. When it has been necessary that a gasket material have a high degree of resistance to acids and alkalis and have a high degree of compressibility, African blue (crocidolite) asbestos was used in place of the white (chrysotile) asbestos. The use of asbestos fibers has always been desirable because of their ready availability and low cost.
Recent concerns about the health hazards associated with exposure to asbestos fibers have resulted in concerted efforts to produce asbestos-free gasket materials. However, this highly desirable objective has not been achieved merely by substituting other fibers for asbestos fibers.
Asbestos-free gasket materials are disclosed in U.S. patent applications Ser. Nos. 953,445; 170,743; and 259,984, which are assigned to the assignee of the present application. The gasket materials of the above-identified co-pending applications are suitable for replacing the prior gasket materials which contain the white (chrysotile) asbestos. While the gasket materials disclosed in the above-identified co-pending applications exhibit substantially similar characteristics and properties to those prior gasket materials which contain white asbestos, they do not possess the greater resistance to acids and alkalis which are characteristic of gasket materials containing African blue (crocidolite) asbestos, nor do they possess an equivalent degree of compressibility.
Furthermore, it has not been proven possible to merely substitute other fibers for the African blue asbestos fibers and still achieve a gasket material of comparable characteristics. By way of example, the substitution of cellulose fibers for crocidolite asbestos will produce a gasket material which will not function effectively at temperatures up to 500.degree. F. and will not possess an acceptable resistance to alkalis.